Injection moulding methods and apparatus

ABSTRACT

An injection moulding apparatus for hollow parts comprises first and second co-operating dies, each die including a first male die core and a female die recess. One of the dies is rotatable about an axis. In a first angular position of the rotatable die, the male die core of the first die co-operates with the female die recess of the second die and the male die core of the second die co-operates with the female die recess of the first die, to define first and second moulds in which half-components may be formed. In a second angular position of the rotatable die, the respective female dies recesses of the first and second dies co-operate to form a third mould in which the half-components may be joined. The apparatus makes use of a single injector differentially controlled for each stage.

[0001] The present invention relates to an apparatus and method forinjection moulding and in particular to an apparatus and method forforming hollow elements such as air filters and fuel tanks for use invehicles.

[0002] A prior art method for producing such hollow elements is know asthe die slide moulding process. In this process, the hollow element isformed in two parts which are moulded separately at spaced locations.The dies are then moved apart and shifted laterally so as to bring thetwo parts into alignment with one another. Originally, the parts wouldbe joined to form the hollow element by hot plate welding or vibrationwelding. More recently bimaterial moulding has been used, with a secondmaterial injected around about the join of the two parts, the secondmaterial connecting and joining the parts on setting.

[0003] The disadvantage of bimaterial moulding is that it requires twoseparate injection devices for injecting the two types of material, onematerial being injected into the moulds to form the parts by a firstinjection device and a second material being injected to join the twoparts together by a second injection device. Likewise, two networks ofinjection channels are required and at least two hydraulic cylinders arerequired to shift the dies and to re-align them correctly. This resultsin an expensive and complex process which is only suitable for highvolume production.

[0004] U.S. Pat. No. 5,221,538 describes an injection moulding machinefor making hollow plastic products comprising two co-operating dies toform moulds for the plastic products. A first die is rotatable about acentral axis and the second die is fixed with respect to rotation aboutthe axis. One of the dies is moveable along the axis so that the diescan be brought together and separated. Each die consists of one male diecore and two female die cavities located radially equidistantly from thecentre axis and at an equal angle (120°) about the centre axis. Therotatable die can adopt two positions, in each of which a male die corefrom the first die co-operates with a female die recess from the seconddie and a male die core from the second die co-operates with a femaledie recess from the first die, allowing two hollow plastic half-productsto be moulded. At the same time, the remaining female dies recesses ofthe respective first and second dies coincide, each containing apreviously moulded half-product. The half-products are joined to formthe final product whilst simultaneously two further half-products aremoulded.

[0005] The apparatus described in U.S. Pat. No. 5,221,538 has certaindisadvantages. Most signficantly, the apparatus of U.S. Pat. No.5,221,538 is only suitable for moulding half-products which are similarsince when the two dies are brought together each male die core must beaccommodated in a corresponding female die recess. Thus, the height ofthe male die core at any given point must always be less than the depthof each female die recess at the corresponding point. In practice, thetwo half-products being moulded must be symmetrical.

[0006] A further problem in the apparatus of U.S. Pat. No. 5,221,538derives from the movement of the rotatable die about a central axis.This makes more complex the attachment of features such as water coolingcircuits and hydraulic circuits (if required) since the necessary pipingmust extend through the machine itself. Otherwise, the pipes may beconnected at a periphery but would have to be flexible to move with thetool, so that the pipes undergo stress and strain and thus increasedrisk of failure.

[0007] Another potential problem with the apparatus of U.S. Pat. No.5,221,538 derives from the fact that two new half-products are mouldedsimultaneously with the joining of two previously formed half-products.This requires a compromise with respect to the process control andparameters (e.g injection pressure and volume) for these steps, where infact the requirements may not be the same.

[0008] The present invention provides apparatus for producing mouldedarticles, comprising: first and second dies, movable towards and awayfrom one another parallel to an axis; the first and second dies eachhaving at least one female die cavity and at least one male die core;means to reciprocally rotate the second die between at least first andsecond angular positions about the axis; and a single injection devicecommunicating with first and second runner drops defined in the firstdie; wherein, in the first angular position, the female die cavity inthe first die receives the male die core of the second die to create afirst mould, the female die cavity in the second die receives the maledie core of the first die to create a second mould, and the first andsecond moulds are in communication with the first and second runnerdrops respectively to receive molten material from the injection deviceto create two moulded parts; and, in the second angular position, thefemale die cavities of the first and second dies are aligned with oneanother to create a third mould which communicates with the first runnerdrop to receive molten material from the injection device whichsurrounds and joins the moulded parts together to produce a wholemoulded material.

[0009] Preferably, the second die comprises a backing member and a bodypivotally attached thereto for rotation about the axis relative to thebacking member and the first die, the body having the at least onefemale die portion and the at least one male die portion of the seconddie.

[0010] The body preferably further includes a first runner associatedwith the male die core and second and third runners associated with thefemale die cavity of the body; wherein, in the first angular position,the first runner connects the first mould to the first runner drop inthe first die and the second runner connects the second mould to thesecond runner drop in the first die; and, in the second angularposition, the third runner connects the third mould to the fist runnerdrop in the first die.

[0011] In the second angular position, the second runner drop in thefirst die is conveniently blanked off by a blanking portion of thesecond die.

[0012] The blanking portion of the second die preferably comprises aheated plate.

[0013] The first and second dies may each have means for receiving themale die core of the other die in the second angular position (at whichthe female die cavities are in alignment). Said means for receiving themale die core may comprise a recess in the respective die.Alternatively, the body attached to the second die may be so sized thatin the second portion, the male die core of the first die is locatedbeyond the marginal edge of the body. Similarly, the male die core ofthe second die may, in the second position be located beyond a marginaledge of the first die.

[0014] In a preferred embodiment, the-means to reciprocally rotate thebody between the first and second angular positions comprises a pistonpivotally secured to the body and a cylinder fixedly secured to thebacking plate.

[0015] Typically, the second die is movable towards and away from thefirst die along the axis under the action of a plurality of cylindersand cooperating pistons.

[0016] The apparatus may further comprise a plurality of co-operatingdowels and bores formed in the first and second dies to hold the dies inalignment in the first and second angular positions.

[0017] Preferably, in the first angular position, the injection deviceis operable to inject a first quantity of molten material sufficient tofill the first and second moulds and, in the second angular position,the injection device is operable to inject a second, smaller quantity ofmolten material sufficient to join the moulded parts together.

[0018] The injection device may comprise a screw driven piston andcylinder.

[0019] The apparatus may further comprise means to inject material oradd a farther component between or into one or both of the moulded partsbefore joining the parts together to form a whole article.

[0020] The present injection also provides a method of producing amoulded article using the apparatus described above comprising the stepsof: with the first and second dies spaced from one another, rotating thesecond die to a first angular position; contacting the first and seconddies whereby the female die cavity of the first die receives the maledie core of the second die and the female die cavity of the second diereceives the male die core of the first die to form first and secondmoulds respectively; injecting molten material from the injection devicethrough the first and second runner drops into the first and secondmoulds to form two moulded parts; separating the fist and second diesrotating the second die to the second angular position; contacting thefirst and second dies whereby the female die cavities, each containing amoulded part, are aligned with one another to form a third mould;injecting molten material through the first runner drop to join themoulded parts together to create a whole moulded article; and separatingthe first and second dies to allow removal of the whole moulded article.

[0021] The method may further comprise the step of injecting material oradding a further component between the two moulded parts before the stepof injecting molten material to join the parts together to form a wholearticle.

[0022] The invention will now be described in detail, by way of exampleonly, with reference to the accompanying drawings in which:

[0023]FIG. 1 is a simplified diagrammatic side view of the apparatus inaccordance with one embodiment of the present invention;

[0024]FIG. 2 is a plan view of one embodiment of a stationary die of theFIG. 1 apparatus, the plan view being shown in the direction of arrowsA-A in FIG. 1;

[0025]FIG. 3 is a plan view of one embodiment of a movable die of theFIG. 1 apparatus, the plan view being shown in the direction of thearrows B-B of FIG. 1;

[0026]FIG. 4 is a plan view similar to FIG. 2 but showing part of themovable die superimposed and in a first position of the mouldingprocess;

[0027]FIG. 5 is a view similar to FIG. 4 showing the movable die in asecond position; and

[0028]FIG. 6 is a schematic view showing a cross-section through twodies of apparatus of the invention brought together in a first stage ofmanufacture;

[0029]FIG. 7 is a schematic view showing a cross-section through twodies of apparatus of the invention brought together in a second stage ofmanufacture;

[0030]FIG. 8 shows apparatus of a second embodiment of the invention ina first operating condition;

[0031]FIG. 9 shows the apparatus of the second embodiment in a secondoperating condition; and

[0032]FIG. 10 shows one part of the apparatus of FIGS. 8 and 9.

[0033] Apparatus 10 for forming hollow elements by an injection mouldingprocess in accordance with the first embodiment of the present inventionis shown in side view and in simplified diagrammatic form in FIG. 1. Theapparatus 10 comprises a first stationary die 12 and a second movabledie 14. The movable die is itself made up of two parts, a pivoting body16 and a backing plate 18. The movable die 14 as a whole is movabletowards and away from the stationary die 12 in a direction parallel toan axis X-X under the action of a plurality of hydraulic cylinders 50.Additionally, the pivoting body 16 is rotatable about the axis X-Xrelative to the stationary die 12 and to the backing plate 18. Mouldsare formed between the mating faces of the stationary die 12 and thepivoting body 16.

[0034] As best seen in FIG. 2, the surface of the stationary die 12which faces the movable die 14 in use, is formed with at least onefemale die cavity 20 and at least one male mould core 22.

[0035] An injection channel 24 connected to a single injection device(not shown) is formed in the stationary die 12 behind the plane of thedrawing in FIG. 2. The injection channel splits into two runner drops todeliver and the open ends of the runner drops 26, 28 can be seen in FIG.2.

[0036] The stationary die 12 is also provided with a recess 30 whichreceives a male die core from the movable die 14 during one stage of theproduction process, described farther below.

[0037] At least three dowels 32 a, b, c are provided in the stationarydie 12 in order to align it with the movable die 14 correctly in use, asdescribed further below.

[0038] The surface of the movable die 14 which faces the stationary diein use is best shown in FIG. 3. The movable die 14 comprises a backingplate 18 to which a pivoting body 16, in this example a substantiallysector shaped element, is rotatably attached at pivot 34. The body 16 isreciprocatable between at least two angular positions under the actionof a hydraulic cylinder 48, fixedly secured to the backing plate 18, andpiston pivotally secured to the body 16.

[0039] The body 16 is formed with a female die cavity 36 and a male diecore 38 which correspond to the male core and female cavity 22, 20 ofthe stationary die 14 respectively so as to form two moulds each forforming one part of a hollow element to be produced.

[0040] The body 16 is also formed with a recess 40 which in one stage ofthe process receives the male die core 22 of the stationary die 12.

[0041] As can best be seen in FIG. 3, the female die cavity 36, male diecore 38 and, where present, recess 40 are arrange on an arc of a circle,the centre of which is of axis (pivot point) 34. The axis 34 is spacedapart from the centre of the body 16 and is ideally located towards onemarginal edge of the body 16, such as towards a corner. The body 16 mayhypothetically describe a body of resolution by complete rotation aboutthe axis 34. Preferably, the body 16 comprises a segment of the body ofrevolution which occupies not more than half, and especially about onequarter of said hypothetical body of revolution. Expressed differentlythe pivot point 34 is, as shown in FIG. 3, advantageously essentiallyexterior to the mould tool itself and this facilitates the connection ofpipes and conduits for water cooling and hydraulic circuits, ifrequired.

[0042] A runner 42, only part of which is shown in the plane of thepaper, is associated with the male die core 38 of the body 16.

[0043] Similarly, two runners 44, 46, only part of which are shown inthe plane of the paper, are associated with the female die cavity 36 ofthe body 16.

[0044] The backing plate 18 includes three bores 33 a,b,c for receivingthe corresponding dowels 32 a,b,c from the stationary die 12 to alignthe two dies in use. The body 16 also includes two through-holes 35, 37through which the dowel rods may pass as discussed further below.Clearly, the dowel rods could be located in the movable die 14 and thebores for receiving the rods could be located in the stationary die 12,or a combination of the two could be used as an alternativeconfiguration.

[0045] In order to form a hollow element using the apparatus shown inFIGS. 1-3, the hydraulic cylinders 50 are retracted so as to bring thestationary die 12 and the movable die 14 into contact with one anothersuch that the female die cavity 20 in the stationery die 12 receives themale die core 38 from the body 16 to form a first mould. Similarly, thefemale die cavity 36 in the body 16 receives the male die core 22 fromthe stationary die 12 to form a second mould.

[0046] As seen in FIG. 4, in this first position the runner 42 in thebody 16 is in communication with the runner drop 26 of the stationarydie 12. Similarly, the runner 44 associated with the female mould cavity36 of the body 16 communicates with the runner drop 28 in the stationarydie 12.

[0047] In this first position, the stationary die 12 and the movable die14 are kept in alignment with one another by the dowels 32 a,b,c beingreceived in the corresponding bores 33 a,b,c. Dowel 32 a passes throughthe hole 35 in the body 16 in order to extend into the bore 33 a in thebacking plate 18.

[0048] An injection device (now shown) such as a screw driven piston isconnected to a common injection conduit 24 which in tun is connected tothe runner drops 26 and 28. The piston is retracted to a first positionin order to draw in sufficient molten material to fill the first andsecond moulds and form both halves of the hollow element. The piston isthen extended in order to inject the molten material through the commonconduit, runner drops 26 and 28 and the runners 42 and 44 and, thus,simultaneously into the first and second moulds in order to create thetwo parts. This is shown in FIG. 6, where two moulded parts 300, 301 canbe seen, the moulded part 300 formed between core 38 of the movable die14 and cavity 20 of the stationary die 12 and the moulded part 301formed between core 22 of the stationary die 12 and cavity 36 of themovable die 14.

[0049] Once both parts 300, 301 have been formed, the hydrauliccylinders 50 are extended so as to separate the stationary die 12 andthe movable die 14. The pivot hydraulic cylinder 48 is operated so as torotate the body 16 about the pivot 34 into the second position shown inFIGS. 5 and 7 in which the two female die cavities 20, 36, eachcontaining a moulded part, are aligned with one another. In this secondposition, the recess 30 in the stationary die 12 receives the male diecore 38 of the body 16 and similarly the recess 40 in the body 16receives the male die core 22 from the stationary die 12.

[0050] Because the respective male die cores 38, 22 are received inrecesses 30, 40, the size and shape of the male die core is notconstrained. In contras to U.S. Pat. No. 5,221,538, the male die cores38, 22 are not, in the second position, accommodated in a female diecavity and so the size and shape of the male die core can be freelyselected. As a consequence, the apparatus of the invention is wellsuited to moulding half-components of differing sizes and shapes whichare joined (in the second position) to form the final component. Forexample, one half-component may be a container of considerable depth andthe other half-component may be a relatively shallow closure for thecontainer. The apparatus of the invention may be used for moulding bothlarge and small components, and because the apparatus does not itselfimpose any restriction on the shape of the components, the componentsmay include more complex features such as bosses, brackets, legs, pipes,and the like.

[0051] The stationary die 12 and the movable die 14 are again kept inalignment in the second position by the dowel rods 32 a,b,c beingreceived in the corresponding bores 33 a,b,c. In this case, the dowelrod 32 a passes through hole 37 in the body 16 in order to extend intothe bore 33 a in the backing plate 18.

[0052] In this second position, the second runner channel 46 associatedwith the female die cavity 36 of the body 16 now communicates with therunner drop 26 in the stationary die 12. The other runner drop 28 isblanked off by a heated plate 52 in the body 16. The heated plate 52keeps the molten material in runner drop 28 in a molten state andprevents a solid plug forming.

[0053] The injection piston (not shown) is now retracted to a secondposition in order to draw in a second, smaller amount of moltenmaterial. The piston is then extended so as to inject the moltenmaterial through the common conduit 24 and into the runner drop 26. Thematerial is able to flow from the runner drop 26 into the second runner46 and thus into the aligned female die cavities 20, 36. The mouldedparts 300, 301 in the cavities 30, 36 abut along facing surfaces. Aroundthe plane of abutment flows the molten material delivered through runner46. When the molten material solidifies it forms a collar 302 whichjoins the two moulded parts 300, 301 together permanently. This isillustrated in FIG. 7 where there is shown a cross-section through afirst moulded part 300 in the female cavity 20 of die 12 and across-section through a second moulded part 301 in the female cavity 36of the die 14. The moulded part 300 has a section which abuts a sectionof the part 301. In the second operating position of the dies(illustrated in FIG. 5) molten material is injected to form the collar302 around the moulded parts 300 and 301.

[0054] Since the amount of molten material required to form the collar302 is significantly less than the amount required to form the two parts300 and 301, the injection piston is retracted to a second positionwhich does not draw in as much material into the cylinder as is drawninto the cylinder when the piston is retracted to the first position.The piston and cylinder device operates according to a computer programand will expel a first amount of material in one stroke and a reducedamount next and then the first amount in the following stroke and so on.Since the half-component forming stage is distinct from the stage ofwhich the half-components are joined, these stages can be separatelycontrolled. This is advantageous, for example, in moulding largecomponents where high injection volumes and pressures may be required inthe half-component forming stages, but much lower injection pressuresand volumes are required in the half-component joining stage.

[0055] Once the two parts 300, 301 have been joined together, the fourhydraulic cylinders 50 are extended so as to separate the stationary andmovable dies 12,14 and allow removal of the complete hollow moulding.The pivot actuator 48 is operated to rotate the body 16 back into thefirst position so that the whole process may be repeated.

[0056] In one particularly preferred variation of the invention the flowof molten material into the respective moulds may be controlled by meansof valve gates. The valve gates are located at the ends of runners atthe point of entry into the respective mould and comprise ahydraulically acted pin which is moveable between a first position inwhich it closes the end of the runner and a second position in which theend of the runner is open. At any given stage in the process, theposition of the valve gate may be chosen as appropriate. Thus, for theformation of the half-components 300, 301 in the first and secondmoulds, one runner (or one series of runners, each runner having a valvegate) may be directed to each of the respective first and second moulds,and the valve gates of each runner will be open. In the second stagewhere the half-components 300, 301 are joined, only one runner (orseries of runners) is required, and the valve gates on the runner (orseries of runners) not required may be closed. The use of valve gatesallows for very precise control of the flow of molten material. Forlarger moulded articles, such as fuel tanks, the use of valve gatesfacilitates the use of more than one runner to a given mould, eachrunner having its own valve gate. For example, as many as six runnersand valve gates may be provided for each mould. The use of valve gatesalso make the heated blanking plate 52 unnecessary since the valve gatescontrol the flow of molten material.

[0057] In a variation (not shown) of the apparatus and method describedabove, an extra stage may be incorporated into the process between thefirst and second stages. That is, before the two moulded parts 300, 301are brought together by alignment of the two female die cavities 20,38,one moulded part 300, 301 could be rotated to a filling position inwhich a material which the hollow element is to contain, (e.g a granularfiltering material) is injected into the two moulded parts 300, 301.Alternatively, an additional component could be disposed within themoulded part 300, 301.

[0058] Subsequently, the second injection process is carried out asdescribed above to provide the molten material to form collar 302joining the two moulded parts 300, 301 together, to form a finishedarticle containing the granular material.

[0059] The apparatus mentioned above can be operated in tandem with amatched second pair of dies, with the first pair and second pairoperationally linked so that when one pair of dies is forming mouldedparts 300, 301 the other pair of dies is forming a collar 302. Thisfacilitates the use of one piston and cylinder device which delivers afixed amount of molten material simultaneously to both pairs of dies ineach stroke (because in each stroke the molten material is used to formboth parts 300, 301 in one pair of dies and also a collar 302 in theother pair of dies).

[0060] In a second embodiment of the present invention, the apparatus is“doubled up” in order to double the rate of production. In thisembodiment, the pivoting body 16 contains first and second pairs offemale die cavities and male die cores, the pairs being arrangedsymmetrically about the pivot axis. Similarly, the stationary diecontains first and second pairs of corresponding male die cores andfemale die cavities also arranged symmetrically about the pivot axis. Inthe first angular position of the pivoting body, the female die cavityand male die core of the first pair in the body are aligned with thecorresponding male die core and female die cavity of the first pair inthe stationary die to form first and second moulds in which the twomoulded parts may be created. At the same time, the female die cavitiesof the second pair of both the body and the stationary die are alignedwith one another to form a third mould in which two previously formedmoulded parts may be joined together to form a whole moulded article.

[0061] When the pivoting body is subsequently moved into the secondposition, the female die cavities of the first pair of both body andstationary die, each female die portion containing a moulded part, arealigned with one another so that the two parts may be joined together toform a whole moulded article. At the same time, the female die cavityand male die core of the second pair in the body are aligned with thecorresponding male die core and the female die cavity of the second pairin the stationary die to form first and second moulds for creating thetwo parts.

[0062] Thus, moulded in each angular position of the pivoting body, twomoulded parts are being moulded on one side of the apparatus and twoparts are being joined together to form a whole part on the other sideof the apparatus. Consequently, a whole moulded article is produced ineach position of the pivoting body, rather than only in the secondposition as with the first embodiment described above. Thus, theproduction range of the apparatus is doubled. Furthermore, a singlepiston and cylinder device delivering a set amount of molten materialcan be used.

[0063] A second embodiment of apparatus is illustrated in FIGS. 8, 9 and10. As with the first embodiment this embodiment comprises a movable die500 pivotally mounted on a backing plate (not shown) and a stationarydie 501. The movable die is pivoted by a piston-and-cylinder arrangement502. However, unlike the first embodiment, the apparatus will have twoinjection cylinders (not shown) each delivering a different material(e.g. two different coloured materials could be delivered). One materialis delivered through a runner drop to a manifold 503 which has twooutlets channels 504, 505. The other material is delivered to a runnerdrop 506. Two male die cores 507, 508 are provided on the stationary die501.

[0064] In the operating condition shown in FIG. 8 a mould is definedbetween a female die cavity. 510 in the movable die 500 and the male diecore 508 of the stationary die 501. A first material delivered throughrunner drop 506 flows along a runner 511 in the movable die 500 andenters the mould formed between female die cavity 510 and male die core508. The material then solidifies and forms a first component. At thesame time a previously moulded component composed of the first materialis present in a female die cavity 512. Molten material of a second typeis delivered via channel 504 in manifold 503 then via a runner 513 inthe die 500 to the cavity 512 where it flows into a volume definedbetween the earlier moulded component and the cavity walls and thensolidifies to form a second component of the moulded part which issubsequently ejected from the mould.

[0065] In the second operating condition shown in FIG. 9 the firstmaterial is delivered from runner drop 506 via runner 514 to a mouldformed between female die cavity 512 and the male die core 507 and afirst component is formed. At the same time second molten material isdelivered via channel 505 in manifold 503 and via a runner 515 in themovable die 500 to the female die cavity 510 where it flows into avolume defined between the previously moulded component of the firstmaterial and the wails of the cavity 510 and then solidifies to completethe moulded part.

[0066] Hydraulic cylinders will move the movable die in a directionperpendicular to its rotational plane between operations to allowseparation between the stationary die 501 and the movable die 500.

[0067] As will be clear to the skilled reader, the present inventionprovides an improved apparatus and method for forming hollow articles byan injection moulding process. The invention provides a relativelysimple apparatus which requires a single injection device and a singlehydraulic cylinder for rotating the body between two different positionsin which different operations can be carried out. It will be apparentthat a number of modifications and variations can be made to theapparatus and method described herein without departing from the scopeof the invention

1. Apparatus for producing moulded articles, comprising: first andsecond dies, movable towards and away from one another parallel to axis;the first and second dies each having at least one female die cavity andat least one male die core; means to rotate the second die about theaxis; and a single injection device communicating with first and secondrunner drops defined in the first die; wherein, in a first angularposition, the female die cavity in the first die receives the male diecore of the second die to create a first mould, the female die cavity inthe second die receives the male die core of the first die to create asecond mould, and the first and second moulds are in communication withthe first and second runner drops respectively to receive moltenmaterial from the injection device to create two moulded parts; and, ina second angular position, the female die cavities of the first andsecond dies are aligned with one another to create a third mould whichcommunicates with the first runner drop to receive molten material fromthe injection device which surrounds and joins the moulded partstogether to produce a whole moulded article.
 2. Apparatus as claimed inclaim 1, wherein the second die comprises a backing member and a bodypivotally attached thereto for rotation about the axis relative to thebacking member and the first die, the body defining the at least onefemale die cavity and the at least one male die core.
 3. Apparatus asclaimed in claim 2, wherein the body further includes a first runnerassociated with the male die core and second and third runnersassociated with the female die cavities of the body, wherein, in thefirst angular position, the first runner connects the first mould to thefirst runner drop in the first die and the second runner connects thesecond mould to the second runner drop in the first die, and, in thesecond angular position, the third runner connects the third mould tothe first runner drop in the first die.
 4. Apparatus as claimed in anyof claims 1 to 3, wherein, in the second angular position, the secondrunner in the first die is blanked off by a portion of the second die.5. Apparatus as claimed in claim 4, wherein the blanking portion of thesecond die comprises a heated plate.
 6. Apparatus as claimed in anypreceding claim, wherein the first and second dies each have a recessfor receiving the male die core of the other die in the second angularposition.
 7. Apparatus as claimed in claim 2, wherein the means toreciprocally rotate the body between the first and second angularpositions comprises a piston pivotally secured to the body and acylinder fixedly secured to the backing plate.
 8. Apparatus as claimedin any preceding claim, wherein the second die is movable towards andaway from the first die along the axis under the action of a pluralityof cylinders and cooperating pistons.
 9. Apparatus as claimed in anypreceding claim, further comprising a plurality of co-operating dowelsand bores formed in the first and second dies to hold the dies inalignment in the first and second angular positions.
 10. Apparatus asclaimed in any preceding claim, wherein in the first angular position,the injection device is operable to inject a first quantity of moltenmaterial sufficient to fill the first and second moulds and, in thesecond angular position, the injection device is operable to inject asecond, smaller quantity of molten material sufficient to join themoulded parts together.
 11. Apparatus as claimed in claim 10, whereinthe injection device comprises a screw-driven piston and cylinder. 12.Apparatus as claimed in any preceding claim, further comprising means toinject material or add a further component into one moulded part beforejoining the moulded parts together to form a whole article. 13.Apparatus as claimed in any preceding claim, wherein the first diecomprises first and second pairs of female die cavities and male diecores, the pairs of male die cores and female die cavities beingarranged one each symmetrically about the pivot axis of the second die;the first die comprises first and second pairs of male die cores andfemale die cavities matching respectively. The first and second pairs ofmale die cores and female die cavities on the second die; wherein: inthe first angular position, the female die cavity and male die core ofthe first pair of the second die are respectively aligned with thecorresponding male die core and female die cavity of the first pair ofthe first die to form the first and second moulds for forming a pair ofmoulded parts; in the second angular position, the female die cavity ofthe first pair of the second die is aligned with the correspondingfemale die cavity of the first pair of the first die to form the thirdmould to receive molten material to surround and join two previouslymoulded parts together to form a whole moulded article; in the firstangular position the female die cavity of the second pair of the seconddie is aligned with the corresponding female die cavity of the secondpair of the first die to form a fourth mould to receive molten materialto surround and join two moulded parts together to form a whole mouldedarticle; and in the second angular position, the female die cavity andmale die core of the second pair of the second die are respectivelyaligned with the corresponding male die core and female die cavity ofthe second pair of the firs die to form fifth and sixth moulds forforming a pair of moulded parts.
 14. A method of producing a mouldedarticle using the apparatus of claim 3, comprising the steps of: withthe first and second dies spaced from one another, rotating the seconddie to the first angular position; contacting the firs and second dieswhereby the female die cavity of the first die receives the male diecore of the second die and the female die cavity of the second diereceives the male die core of the first die to form the first and secondmoulds respectively; injecting molten material from the injection devicethrough the first and second runners into the first and second moulds toform two moulded parts; separating the first and second dies; rotatingthe second die to the second angular position; contacting the first andsecond dies whereby the female die cavities, each containing a mouldedpart are aligned with one another to form a third mould; injectingmolten material through the first runner drop to join the moulded partstogether to create a whole moulded material; and separating the firstand second dies to allow removal of the whole moulded article.
 15. Amethod as claimed in claim 14, further comprising the step of injectingmaterial into at least one moulded part before injecting molten materialto join the moulded parts together to form a whole article.
 16. A hollowarticle produced by the apparatus of any of the claims 1 to
 13. 17. Ahollow article produced by the method of claim 14 or
 15. 18. Apparatussubstantially as hereinbefore described with reference to theaccompanying drawings.
 19. A method substantially as hereinbeforedescribed with reference to the accompanying drawings.
 20. A method ofmoulding an article comprising the steps of: (a) bringing together afirst die with a second die in a first relative position to form firstand second moulds, the first mould being defined between a male die coreof the first die and a female die cavity of the second die and thesecond mould being defined between a male die core of the second die anda female die cavity of the first die; (b) using a single injectiondevice to deliver a first amount of molten material which is relayed toboth of the first and second moulds to form first and second mouldedparts; (c) separating the first die from the second die to remove themale die cores from the female die cavities whilst retaining the firstand second moulded part in the female die cavities; (d) moving thesecond die relative to the first die to a second relative position inwhich the female die cavity of the first die aligns with the female diecavity of the second die; (e) bringing together the first and seconddies in the second relative position to bring together facing surfacesof the first moulded part situated in the female die cavity of the firstdie and the second moulded part situated in the female die cavity of thesecond die, the female die cavities of the first and second diestogether defining a third mould in which both previously moulded partsare located; (f) using the single injection device to deliver a secondamount of molten material to the third mould, which molten materialsurrounds a part at least of each previously moulded part and thensolidifies to connect and joint together the two previously mouldedparts to form a single moulded entity; (g) removing the single mouldedentity from the separated first and second dies; (h) moving the firstand second dies back to the first relative position and bringing thefist and second dies together to commence a further cycle and form asecond moulded entity; and wherein the first amount of materialdelivered by the single injection device to the first and second mouldsis different to the second amount of material delivered by the singleinjection device to the third mould and the single injection device iscontrolled by electronic control means which controls the amount ofmolten material delivered by the single injection device having regardto whether the molten material is to be delivered to the first andsecond or to the third mould.
 21. A method as claimed in claim 20comprising additionally the steps of: delivering the molten materialexpelled by the single injection device through first and second runnerdrops in the first die; delivering the molten material to the first andsecond moulds by first and second runners in the second die, the firstand second runners aligning with the runner drops in the first die toreceive molten material therefrom only when the first and second diesare in the fist relative position; and delivering the molten material tothe third mould by a third runner in the second die, the third runneraligning with a runner drop in the first die to receive molten materialtherefrom only when the first and second dies are in the second relativeposition.
 22. A method as claimed in claim 21 or claim 22 comprising thestep of: moving the first and second dies from the first relativeposition to the second relative position and subsequently back from thesecond relative position to the first relative position by rotating thesecond die about an axis.
 23. A method as claimed in claim 22 comprisingthe step of: using a single actuator to rotate the second die about theaxis.
 24. A method as claimed in any one of claims 20 to 23 comprisingthe step of: using the same single injection device to deliver moltenmaterial of the same composition to the first and second moulds and tothe third mould.
 25. A method of moulding an article comprising thesteps of: (a) bringing together first and second dies in a firstrelative position to form first and second moulds, the first mould beingdefined between a male die core of the first die and a female die cavityof the second die and the second mould being defined between a male diecore of the second die and a female die cavity of the first die; (b)injecting molten material into both the first and second moulds to formfirst and second moulded parts; (c) separating the first and second diesto remove the male die cores form the female die cavities whilstretaining the first and second moulded parts in the female die cavities;(d) moving the first die relative to the second die to a second relativeposition; (e) bringing together the first and second dies in the secondrelative position to bring together facing surfaces of the first mouldedpart situated in the female die cavity of first die and the secondmoulded part situated in the female die cavity of the second die, thefemale die cavities of the first and second dies together defining athird mould in which both previously moulded parts are located; (f)injecting molten material into the third mould, the molten materialsurrounding a part at least of each previously moulded part andsolidifying to connect together the two previously moulded parts to forma single moulded entity; (g) separating the first and second dies andremoving the single moulded entity from the separated first and seconddies; (h) moving the first and second dies back to the first relativeposition and bringing the first and second dies together to commence afurther cycle and form a second moulded entity; wherein the methodcomprises additionally the steps of: delivering the molten material tothe fir second and third moulds through a first and second runner dropwhich extend through the first die; delivering the molten material tothe first and second moulds by first and second runners in the seconddie, the first and second runners aligning with first and second runnerdrops of the first die to receive molten material therefrom only whenthe first and second dies are in the first relative position; anddelivering molten material to the third mould by a third runner in thesecond die, the third runner aligning with a runner drop of the firstdie to receive molten material therefrom only when the first and seconddies are in the second relative position.
 26. A method as claimed inclaim 25 comprising the step of: moving the first and second dies fromthe first relative position to the second relative position andsubsequently back form the second relative position to the firstrelative position by rotating the second die about an axis.
 27. A methodas claimed in claim 25 or claim 26 comprising the steps of: using asingle runner drop to deliver molten material to one of the first andsecond runners and also to the third runner in the second die.
 28. Amethod as claimed in any one of claims 25 to 27 comprising the step of:using apart of the surface of the second die to seal off at least one ofthe runner drops in the surface of the first die whilst molten materialis delivered to the third mould.
 29. A method as claimed in claim 28comprising the step of: heating the part of the surface of the seconddie used to seal off the aperture in the surface of the first die.
 30. Amethod of moulding an article using apparatus which comprises: a firstdie; a second die; means to rotate the second die about an axis; meansto move at least one of the first and second dies translationallyparallel to the axis; and injection means for delivering molten materialunder pressure; the method comprising the steps of: a) bringing thefirst and second dies together in a first rotational position in whichthe first and second dies define between them a first mould; b) usingthe injection means to deliver a first amount of molten material; c)relaying the first amount of molten material to the first mould via afirst runner provided in the second die; d) allowing the molten materialto cool and solidify in the first mould to form a first component of thearticle; e) separating the first and second dies by moving at least oneof the dies translationally; f) rotating the second die relative to thefirst die once separated therefrom; g) bringing the first and seconddies together in a second rotational position in which the first andsecond dies define between them a second mould in which the previouslyformed component is located; h) using the injection means to deliver asecond amount of molten material to the second mould; i) relaying thesecond amount of molten material to the second mould via a second runnerprovided in the second die; j) allowing the molten material to cool andsolidify in the second mould to form a second component of the articlesurrounding the fist component.
 31. A method as claimed in claim 30wherein: the apparatus used comprises at least one runner drop extendingthrough the first die which receives molten material delivered from theinjection means; the first runner in the second die aligns with a runnerdrop in the first die only in the first rotational position of thesecond die; and the second runner in the second die aligns with a runnerdrop in the second die only in the second rotational position of thesecond die.
 32. A method as claimed in claim 30 or claim 31 where thefirst amount of molten material delivered by the injection means isdifferent to the second amount of molten material delivered thereby. 33.A method as claimed in any one of claims 31 to 33 wherein the injectionmeans comprises first and second injectors and wherein the firstinjector is used to deliver the first amount of a first molten materialto the first mould and the second injector is used to deliver the secondamount of second molten material to the second mould, the second moltenmaterial being different to the first molten material.
 34. A method asclaimed in claim 33 wherein: the first molten material is deliveredthrough a first runner drop in the first die which aligns with the firstrunner in the second die in the first rotational position of the seconddie; and the second molten material is delivered through a second runnerdrop in the first die which aligns with the second runner in the seconddie in the second rotational position of the second die.
 35. A method asclaimed in any one of claims 30 to 32 wherein: the injection meanscomprises a single injection; the first die comprises first and secondrunner drops; the first amount of molten material is delivered throughthe first runner drop which aligns with the first runner in the firstrotational position of the second die; and the second amount of moltenmaterial is delivered through the second runner drop which aligns withthe second runner in the second rotational position of the second die.